In many modern production facilities, conveyor systems play an integral role in moving articles in process from location to location. Such systems are of particular benefit in the food processing and article packaging industries, where it necessary to transport articles to and from different areas of the production facility to undergo various manufacturing/packaging operations. Due to constraints, such as limitations in floor space, alterations in the direction of travel of the belt must be made by providing curves or bends in the conveyor system. This permits the movement of articles in virtually any direction required or to any specific location in the facility.
With regard to the use of such curves or bends, one significant problem encountered is a substantial increase in the drag force experienced by a modular link conveyor belt, particularly as linear speed increases. It is known that when such a side-flexing conveyor belt rounds a curve or bend, the inner guide or side links compress and the outside guide links expand relative to one another. This simultaneous expansion and compression that also extends to the links making up the body of the belt, places the belt in lateral tension along the radius of the curve. Such tension has the deleterious effect of causing the outer guide links to press against the outer guide rail (which is usually a curved, stainless steel channel). Contact between these links traveling at a high speed and this channel create various "hot spots." As the linear speed of the belt is increased, a concomitant increase in the frictional drag force and related heat generation occurs. Left unchecked, this heat will eventually cause the plastic depending arm of the side link to soften, which can lead to system failure.
Even when operating at lower speeds, this frictional drag serves to reduce system efficiency, as more power is required to overcome this force. Additionally, the side links of the conveyor belt wear more rapidly, which further increases the incidence of link or belt failure. These difficulties inevitably lead to costly production downtime.
Conventional attempts to reduce this troublesome drag force have not been particularly successful. For instance, providing a constant source of lubrication to the curved guide rails can temporarily reduce friction and the resulting drag force. However, the presence of industrial lubricants is undesirable for many production operations, such as food processing, as the food product is subject to contamination. Additionally, lubricants readily trap loose food product and create an unsanitary residue that provides a breeding ground for bacteria or the like. Furthermore, the frequent washing of the system required to meet governmental regulations will necessitate re-application of the lubricant. Thus, even if the lubricant is ruled safe to be around the food product, the cost of such frequent re-application to the rails is prohibitive.
One early proposal for reducing the deleterious drag force is taught in U.S. Pat. No. 3,094,206 to Stewart. The system described therein includes a flexible wire conveyor belt having a pair of centrally-located depending legs with shoulders. The shoulders track along a series of rollers secured near the center of the conveyor frame. While this proposal attempts to reduce the drag force by substituting rollers for the conventional passive or static guide rail, it is apparent that such a design lacks the stability that is required in modern operations, especially during high speed belt operation. Specifically, the presence of a single guide rail in the center fails to consistently maintain the belt flat, which permits the belt edges to flex upwardly and away from the conveyor support frame.
Modern efforts to improve the tribological characteristics in modular-type conveyor systems have moved away from the teaching of the '206 patent and instead have sought to alleviate the problem by redesigning the conveyor belt itself. Most, if not all, of such proposals involve the attachment of rollers directly to the underside of the belt to reduce the drag force. During operation, these rollers track along one or more passive guide rails in an attempt to guide the belt along the curve with less friction. For example, U.S. Pat. No. 5,573,105 to Palmaer discloses a modular link conveyor belt having a plurality of rollers carried under the belt. These rollers also engage a center rail. A similar example of such a design is U.S. Pat. No. 5,038,925 to Chrysler, which teaches the use of split rollers mounted along the peripheral edge of the conveyor belt for engaging a passive guide rail.
While such proposals offer some improvement over earlier approaches, such as the concept of applying a lubricating substance, several limitations remain. The complexity and expense of providing a conveyor belt with rollers is the main drawback, since the cost of construction more than doubles. Furthermore, with the number of rollers increasing by ten/twenty fold or more, the chances of failure leading to downtime are greatly increased. Also, from a sanitary viewpoint, these extra rollers increase the problem of cleaning the belt to meet governmental standards.
Rather than placing rollers on the underside of the belt, still others propose similar modifications along the exterior of the conveyor belt. For example, in U.S. Pat. No. 3,946,857 to Fraioli, Sr., a series of rollers are attached along the peripheral edges of the conveyor belt for tracking along a passive guide rail. It should be readily apparent from viewing this proposed design that similar limitations remain; namely, complexity and cost of design, increased incidence of belt failure, and complicated cleaning requirements.
Thus, a need exists for a side flexing, modular conveyor system with improved operating characteristics, particularly with a view toward reducing or substantially eliminating the drag force experienced by the belt as a curve or bend is traversed. Such an improved system would be both simple in design and inexpensive to construct and maintain. Furthermore, the system would provide the belt with improved stability to ensure that horizontal curves or bends are smoothly and efficiently negotiated, without experiencing any significant vibration or chatter.